Apparatus for measuring density of a thixotropic fluid



oct, 19, 194s.

W. `E. BARNES APPARATUS FOR MEASURING DENSITY OF A THIXOTROPIC FLUID 'Filed Aug. 22, 1945 2 Sheets-Sheet 2 IN VEN TOR TVILLIAM E. BARNES ATTORNEYS Patented oel. 1 9, 194s APPARATUS FOB MEASURING DENSITY F A THIXOTROPIC FLUID William E. Barnes, Beaumont, Tex., assignor to Sun Oil Company, Philadelphia, Pa., a corporay tion of New Jersey Application August 22, 1945, Serial No. 612,096

' 2 Claims.

1 e, This invention relates vto means for determinlng the density of a iluid and is particularly adapted for use in determining the density of a thixotropic iluid such as the drilling mud used in the rotary drilling of wells. In drilling wells by the rotary method, drilling mud is circulated down through the drill pipe and up through the annular space between the drill pipe and borehole. The mud functions to remove the cuttings from the borehole. to prevent caving of the borehole wall and to provide suillcient hydrostatic pressure to overcome the pressure of the formations penetrated. A close control of the density of the drilling mud throughout the drilling operation is generally highly desirable. On the one hand, it is necessary that the weight .of the drilling mud be sufficient to provide a hydrostatic pressure adequate to hold back fluids such as gas or water in the formations encountered in order to prevent a blowout of the borehole. On the other hand, if the drilling mud becomes too heavy, the drilling iiuid may be continuously forced into one or more of the formations penetrated resulting in the condition known as "lost circulation." During the course of the drilling frequent adjustment of the weight of the mud, as by the addition of weighting materials, is required to meet the varying conditions encountered. For instance, upon penetration of a gas sand, the mud stream may become considerably lighter due to absorption of gas, in which case it is important that the change in density of the mud fluid be detected immediately so that proper steps may be taken to increase the weight of the circulating mudand prevent a blowout. In some cases a variation in mud weight .of only a small fraction of a pound per gallon may be sutliclently important to constitute the difference between satisfactory and unsatisfactory drilling progress. It is evident, therefore. that a continual accurate measurement of the mud.density during the drilling operation is highly desirable.

It is an object of the present invention to provide apparatus for continuously measuring the density of a circulating fluid, which apparatus is designed specifically to operate on a thixotropic iluld such as drilling mud and to minimize inaccuracies of measurement tending to arise as a result of its thixotropic character.

The density measuring apparatus according to the invention utilizes the diiferencein pressure on two flexible diaphragms, vertically spaced within the fluid, as an indication of the fluid density. 'While other density measuring devices operating on a similar principle have been known heretofore, such devices have not been designed so as to be capable of accurate measurement when the uid being measured has a thixotropic character, i. e. the tendency to undergo gelatin when quiescent but readily to revert to a iiuid state .upon agitation. I have found that for accurate measurement of the density of a thlxotropic uid such as drilling mud, the aforesaid diaphragms should be placed in la vertical position within the fluid and further that they should be so positioned as to permit free ow of the uid across the face of the diaphragm. This arrangement minimizes gelation of iluid adjacent to the diaphragms so that inaccuracies of measurement resulting from the thixotropic nature of the drilling mud are eliminated or minimized.

For a more complete understanding of the invention, reference may be had to the accompanying drawings in which:

Figure 1 is an elevational View of one form of the assembled apparatus with some parts sectioned to show detalls. l

Figure 2 isa view vtaken on the line 2-2 of Figure 1. l

Figure 3 is an enlarged sectional view of the arrangement of diaphragm and housing.

Referring to the drawings in which like numerals designate like elements, a passageway for the flow of the fluid lsillustrated in Figure 1 as a 1 vertical chamber i0 having a iluid inlet Il at the topand a fluid outlet I2 at the bottom. `A minor stream of the drilling mud preferably is diverted from the main stream returning from the well bore and is passed continuously through inlet line Il into the top of vertical chamberv I ll.`

Means are provided for maintaining the level of the uid in the upper part of chamber I0, as shown at I3. Such means may comprisean overow line I4 connected to outlet line i2 and having a point of overow for the iluid at the desired level.

Associated with the passageway or chamber ,are a pair of vertically spaced apart housings 15a chamber and is secured to the wail by means of bolts I'I. The diaphragm Ilia extends over the opening and the edge of the diaphragm is anchored lbetween the housing Ia and the wall. In order t0 minimize the eiect of the wall as an obstruction to the free flow of fluid across the diaphragm, the wall thickness should be small relative to the Width of the opening over which the diaphragm I6a ls positioned, and the edge of the wali may be beveled as illustrated at 8.

A differential pressure indicating device is rovided for measuring the difference in pressures exerted on the diaphragms by the fluid as an indication of the density of the uid. For this purpose any suitable type of differential pressure device may be employed. As diagrammatically illustrated in Figure 1, the device may comprise a U-tube I9 having enlarged section 20 and containing mercury 2 I The housings I5a and I5b are in communication with separate legs of the U-tube I9 by means of lines 22a and 22h, respectively. Lines 22a and 22h, as well as the space enclosed by each of the housings with its diaphragm, are filled with a liquid such as water or oil for transmitting the pressure exerted by the drilling fluid on each diaphragm to the differential pressure device. Enlarged section of the U-tube contains oat 23 which is adapted to oat at the surface of the mercury 2| and to rise and fall in accordance with changes in its level. Float 23 is connected with scriber 24 through any conventional or suitable means for actuating the scriber in accordance with the movement of the float. Associated with scriber 24 is chart 25 driven by a clock mechanism and calibrated to show the density of the fluid being measured. Numeral 26 indicates an instrument panel (shown in broken lines) upon which the differential pressure indicating and recording device may be mounted.

As further shown in Figures 1 and 2, stirring means are provided for 'agitating the fluid within the passageway or chamber l0 to prevent gelation of fluid adjacent diaphragms Iia and 13b. Such means comprise a vertical shaft 21 centered withinthe chamber and supported for rotation in bearing 28 and carrying one or more blades 29 for stirring the uid. The upper part of shaft 21 is supported by means of bearing 30 and support arm 3|. In the upper part of the chamber a horizontal shaft S2, supported by bearings33, carries a paddle wheel 34 fixed thereon. The stirring said different levels.

element, comprising vertical shaft 21 with blades 29 attached, is geared to horizontal shaft 32 by means of worm gear 35 and worm 36. Fluid inlet line Il is placed with its outlet over paddle wheel 34 but o5 center so that the incoming fluid will cause paddle wheel 34 to rotate and thereby drive the stirring element. This prevents gelation of 4 fluid Within'the chamber thus permitting accurate measurement of the fluid` density at all times.

What I claim and desire to protect by Letters Patent is:

1. Apparatus for measuring the density of a thixotropic material such as drilling mud iiuid which comprises a chamber for the passage of the fluid therethrough, said chamber bein-g designed to maintain a body of fluid therein, a pair of pressure responsive flexible diaphragms vertically spaced apart with respect to the chamber in order to be responsive to the different pressures of the fluid existing at different levels within the chamber, agitating means within the chamber and power means for operating the agitating means in order to minimize gelation, adjacent the diaphragms, resulting from the thixotropic nature of the fluid, Va differential pressure indicating dcvice exterior-ly of the chamber and means controlled by each of said diaphragms to operate said device in accordance with the difference in pressures obtaining at the said different levels.

2. Apparatus for measuring, the density of a hixotropic material such as drilling mud fluid which comprises a chamber for the passage of the fluid therethrough and being designed to maintain a body of uid therein,-said chamber having a pair ofapertures in its wall which are spaced apart vertically thereof, a diaphragm secured adjacentto and closing each aperture, said diaphragms being thus positioned at difierent levels and each being responsiveto the pressure of the fluid obtaining at its level, agitating means within the chamber and power means for operating the agitating means in order to minimize gelation, adjacent the diaphragms, resulting from the thixotropic 4nature of the fluid, a difierential pressure indicating device exterlorly of the chamber and means controlled by each of said diaphragms to operate said device in accordance with the dilerence in pressures obtaining at the WILLIAM E. BARNES.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number 

